2. What is a suitable electrolyte/electrolyte? The author still uses sodium ion and electrolyte system commonly used in lithium ion batteries. According to the electrochemical data, there may be electrolyte side reaction, and the cycle stability and life of the battery are very poor. It is unknown whether it is because of electrolyte or other reasons.
3. Such heterogeneous reaction is inherently unfavorable to battery materials. The smaller the structural change of battery materials, the better. Solid solution reaction (such as lithium cobaltate, ternary, etc.) is preferred. ), and the two-phase reaction with little structural change is the second choice (LFP is a little different, but some studies show that the "two-phase" reaction of nano-LFP is still a solid solution reaction). Heterogeneous reaction is the least ideal choice. The voltage platform of multiphase reaction is unstable, and the material structure changes greatly, which will become worse after many cycles. So there are many materials that can react with three or four lithium ions, such as lithium vanadate series, but why are they not widely used? It is because there are all kinds of problems.
4. Low voltage. This is another fatal problem. If the voltage is low 1.5 volts, the energy density will be reduced by 1.5 times (assuming the capacity is unchanged). Because it is a carbonyl C-O system, the voltage is inherently low. In the sodium ion system, Japanese Yamada can get a voltage as high as 3.8V by using ferric sulfate/ferrous system. Although the capacity of that system is lower, the energy density is not much worse than this system. (This article claims that the positive electrode can reach 726wh/kg, hehe, it depends on how to understand this number. )
5. The low density of organometallic compounds is a fatal defect. Low density leads to low volume capacity/energy density, and the battery volume will become larger. This runs counter to the direction that the battery is getting thinner and smaller. Whether it is installed in a mobile phone or a car, the bulk of the battery is mostly an unacceptable defect. The biggest selling point of this sodium ion battery is its cheapness. But because of its too many performance slots, the real value that this cheap price can bring should also be questioned. Lithium resource is actually not an extremely scarce resource. At present, the high price is mainly due to market factors and insufficient development, as well as geographical factors. Most of the cheap and high-quality salt lakes are in South America, and the development cycle is relatively long. The cost of lithium ore route is high, but there is still a lot of room for technological progress; More importantly, lithium is a recyclable material, but the current technology and investment have not reached the scale. I believe that if this aspect is better integrated in the future, the advantages of lithium ion will still be far greater than that of sodium ion. Moreover, there are still many places worthy of breakthrough in the field of lithium ion, such as directly using lithium metal as the negative electrode. If we break through this piece, the performance of lithium batteries will be greatly improved. Cheaper high-energy systems such as lithium sulfur will also be unlocked.